1. Field of the Invention
The present invention relates to a mobility management system, and a mobile node, a mobility management method, and a mobility management program used in the system and, more particularly, to a mobility management system for improving the mobility of a mobile node performing telecommunications on a network for telecommunications of the packet switching system like Internet, and a mobile node used in the system, a mobility management method, a mobility management program, and a mobility management node.
2. Related Background Art
FIG. 1 is an illustration for explaining a network architecture of a conventional packet telecommunication system. In the drawing a cloud indicates a network having an arbitrary topology consisting of a plurality of nodes and links. The nodes called routers in the cloud hold routing information through action of a routing control protocol such as OSPF (Open Shortest Path First) or the like.
Each router is able to accurately forward a packet addressed to any node other than its own node, to an area where the destination node exists. This cloud routing the packet in this way on the basis of the address system of IP (Internet Protocol) will be herein after called an IP packet telecommunication system.
The same figure shows a mobile node MN, a home agent HA, a mobility agent MA1 and a mobility agent MA2 being nodes that perform mobility management, and access routers AR1-AR8.
The mobile node MN is a node that performs communications with another node while changing a connected link from one to another with movement. The home agent HA is a node that provides a home link to the mobile node MN.
The access routers AR1-AR8 are nodes that provide foreign links to the mobile node MN. A correspondent node CN is a node that performs communications with the mobile node MN.
The mobility agents MA1 and MA2 are nodes that have their respective, definite service areas and perform the forwarding operation of a packet addressed to the mobile node MN under connection with an access router AR in the service area. The service areas of the mobility agent MA1 and the mobility agent MA2 are indicated by respective dashed lines in the same figure. These mobility agents MA1 and MA2 function as nodes performing the mobility management.
There exist the access routers AR1-AR4 in the service area of the mobility agent MA1. On the other hand, there exist the access routers AR5-AR8 in the service area of the mobility agent MA2.
The mobile node MN in motion between foreign links uses a home address used in the home link, and a link c/o address (Care of Address; which will be hereinafter referred to as CoA) used in each foreign link. The home address is an address that is continuously used even with change of a connected link to another. CoA is an address that is acquired at every change to a connected link and that specifies the mobile node in the connected link.
The following will describe the operation of the conventional “Hierarchical Mobile IPv6” with reference to FIG. 2. The mobile node MN moves away from the home link to an foreign link, and {circle around (1)} receives Router Advertisement (hereinafter, RA) sent from an access router.
{circle around (2)} The mobile node MN adds a token of a radio interface of its own node to a prefix (an identifier of the subnet) included in RA, to configure CoA (CoA3 in the figure) (stateless address autoconfiguration). The token herein refers to a hardware address for uniquely identifying a radio interface.
{circle around (3)} The mobile node MN sends a packet called Binding Update (hereinafter, BU) including binding of CoA and the home address, to a mobility agent (the mobility agent MA1 in the figure). The mobile node MN is able to know an address of the mobility agent from the information in RA sent from the access router.
{circle around (4)} The mobility agent, receiving the BU packet, records the binding information in the BU packet, in its cache.
{circle around (5)} The mobility agent sends a binding acknowledgement received, to the mobile node MN.
{circle around (6)} When receiving the binding acknowledgement from the mobility agent, the mobile node MN sends to the home agent HA a BU packet including binding of the address of the mobility agent and the home address.
{circle around (7)} The home agent HA, receiving the BU packet, records this binding information in its cache.
FIG. 3 shows a state in which the foregoing caches are present at the home agent HA and at the mobility agent. In the same figure, the correspondent node CN is a node that performs communications with the mobile node MN. When the correspondent node CN sends a packet I directed to the home address of the mobile node, the packet I is normally routed by the routers in the network. When the packet I arrives at the home link of the mobile node MN, it is captured at the home link by the home agent HA. The home agent HA creates an IP packet a destination of which is the address (the address of the mobility agent) bound to the home address of the mobile node MN as the destination of the packet I, and stores the packet I in a payload portion of the IP packet. The method of storing another packet in the payload portion of a certain packet in this way is called tunneling and such a packet is called a tunneling packet. The tunneling packet II prepared according to the above procedure by the home agent HA is delivered to the mobility agent by the routers in the network. The mobility agent takes the packet I out of the payload of the tunneling packet II and searches data on the cache for the home address of the mobile node MN which is the destination of the packet. Then the mobility agent creates a new tunneling packet III a destination of which is the CoA bound to the home address of the mobile node MN, stores the packet I in the payload portion of the tunneling packet III, and sends the tunneling packet III. The tunneling packet III is routed to the mobile node MN, so that the mobile node MN can receive the tunneling packet III directed to the CoA and process the packet I stored in the tunneling packet. The above procedure permits the mobile node MN to receive the packet directed to the home address of the mobile node MN, on the foreign link where the mobile node MN visits.
Thereafter, the mobile node MN notifies the mobility agent of the binding of the home address and CoA by the BU packet every time the mobile node MN acquires a new CoA with movement between eternal links in the service area of the mobility agent. When the mobile node changes the link from one to another in the service area of the same mobility agent, it needs only to notify the mobility agent of CoA of a new link, so as to be able to establish the aforementioned packet forwarding route of the correspondent node CN→the home agent HA→the mobility agent→the mobile node MN, while notifying the home agent HA of nothing.
On the other hand, when the mobile node MN moves between access routers AR of different mobility agent service areas and acquires a new CoA, it notifies the mobility agent of the binding of the home address and the CoA by the BU packet. When receiving a binding acknowledgement from the mobility agent, the mobile node MN notifies the home agent HA of the binding of the home address and the address of the mobility agent by the BU packet. As described, when the mobile node moves between access routers AR of different mobility agent service areas, it sends the BU packet to each of the new mobility agent and the home agent HA, so as to be able to establish a packet forwarding route of the correspondent node CN→the home agent HA→the mobility agent→the mobile node MN.
The basic operations of the home agent and the mobile node in Mobile IPv6 are disclosed by, for example, D. B. Johnson, C. Perkins and J. Arkko in “Mobility Support in IPv6,” draft-ietf-mobileipv6-mobileip-18.txt, July 2002 (work in progress). http://ww.ietf.org/internet-drafts/draft-ieif-mobileip-ipv6-18.txt>.
Further, the basic operation of Mobility Anchor Point (MAP) in Hierarchical Mobile IPv6 is disclosed by H. Soliman and K. El-Malki in “Hierarchical MIPv6 Mobility Management (HMIPv6),” draft-ietf-mobileip-hmipv6-06.txt, July 2002 (work in progress). <http://ww.ietf.org/internet-drafts/draft-ietf-mobileip-hmipv6-06.txt>.